Feedback control of external MHD modes using high speed FPGA computing on the HBT-EP tokamak
Abstract
Stabilization of external kink modes using conductive walls and active feedback is a promising route to high performance tokamak operation. We present results from experiments involving 20 poloidal field sensors used to provide feedback signals for 40 in-vessel control coils, which directly face the plasma. Signals are processed digitally using high-speed FPGA's which detect the n = 1 component of the sensor field, incorporate phase compensation, and rotate the toroidal phase of the applied control fields. Over-all feedback loop latency is 10 msec. The versatility of this system allows a multitude of rapidly realizable experimental configurations to explore the limits of mode control feedback algorithms. To date, we have observed suppression and excitation of m/n =3/1 external modes dependent on the toroidal phase of the control field in closed loop experiments. A systematic study of the effects of latency produced results in good agreement with model predictions for feedback loop performance. Kink mode rotation is observed to change in these experiments and can be driven far above and below the natural mode rotation rate. In addition, open loop m/n = 3/1 helical rotating perturbations were applied to RWM stable and unstable plasma configurations, and the plasma response to these perturbations measured.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- November 2004
- Bibcode:
- 2004APS..DPPBP1130K